This invention generally relates to gas turbine rotor blades and more particularly to cooling the trailing edge tip region of turbine rotor blades.
Turbine rotor blades of certain varieties operate in extremely high temperature environments. In order to achieve adequate service life, the blades typically include hollow airfoils so that cooling fluid (usually air) can be routed to interior cavities and reduce the high surface temperatures. An area that is troublesome in this regard is the blade tip, the radial extremity of the blade, and particularly, the trailing edge region of the blade tip.
The proximity of the blade tip to a circumscribing shroud makes the blade tip difficult to cool. The shroud defines a flow path for the operating fluid of the turbomachine. The contiguity of the shroud and the blade tip minimizes the leakage of hot operating fluid past the tip which correspondingly improves turbine efficiency. A tip cavity comprising a recessed tip cap surrounded by radially extending side walls provides a means for achieving minimal tip clearance while at the same time assuring adequate blade tip cooling. Cooling fluid, exhausted from the interior cavity, is fed into the tip cavity through holes in the tip cap, cooling the radially extending side walls as well as the tip cap surface.
The trailing edge tip of the blade is particularly thin, lacking the appropriate wall thickness to extend the tip cavity to the trailing edge tip corner. In order to prevent oxidation of the trailing edge tip, additional cooling holes extending radially through the trailing edge tip to the internal cavity may be provided. However, the penalty of this arrangement is a reduction in cooling air to the trailing edge region of the blade resulting in higher operating temperatures which enhances blade deterioration.
For the foregoing reasons, there is a need for a blade tip design having improved blade tip trailing edge cooling.